Patch the c-ares resolver binding to support asking for both
IPv4 and IPv6 addresses when IPv6 is enabled.

This is a workaround for the missing ares_getaddrinfo() and is a lot
easier to implement.

Note that as long as c-ares returns IPv4 addresses when IPv6 addresses
were requested but missing, this will cause a host's IPv4 addresses
to occur twice in the DNS cache.
---
 lib/hostares.c |   29 +++++++++++++++++++++++------
 lib/hostasyn.c |   56 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 lib/urldata.h  |    2 ++
 3 files changed, 81 insertions(+), 6 deletions(-)

diff --git a/lib/hostares.c b/lib/hostares.c
index e31a677..85c91ab 100644
--- a/lib/hostares.c
+++ b/lib/hostares.c
@@ -401,13 +401,30 @@ Curl_addrinfo *Curl_getaddrinfo(struct connectdata *conn,
     Curl_safefree(conn->async.hostname);
     conn->async.hostname = bufp;
     conn->async.port = port;
-    conn->async.done = FALSE; /* not done */
-    conn->async.status = 0;   /* clear */
-    conn->async.dns = NULL;   /* clear */
+    conn->async.done = FALSE;   /* not done */
+    conn->async.status = 0;     /* clear */
+    conn->async.dns = NULL;     /* clear */
+    conn->async.temp_ai = NULL; /* clear */
 
-    /* areschannel is already setup in the Curl_open() function */
-    ares_gethostbyname(data->state.areschannel, hostname, family,
-                       (ares_host_callback)ares_query_completed_cb, conn);
+#ifdef ENABLE_IPV6 /* CURLRES_IPV6 */
+    if(family == PF_UNSPEC) {
+      conn->async.num_pending = 2;
+
+      /* areschannel is already setup in the Curl_open() function */
+      ares_gethostbyname(data->state.areschannel, hostname, PF_INET,
+                         ares_query_completed_cb, conn);
+      ares_gethostbyname(data->state.areschannel, hostname, PF_INET6,
+                         ares_query_completed_cb, conn);
+    }
+    else
+#endif /* CURLRES_IPV6 */
+    {
+      conn->async.num_pending = 1;
+
+      /* areschannel is already setup in the Curl_open() function */
+      ares_gethostbyname(data->state.areschannel, hostname, family,
+                         ares_query_completed_cb, conn);
+    }
 
     *waitp = 1; /* expect asynchronous response */
   }
diff --git a/lib/hostasyn.c b/lib/hostasyn.c
index 127b8d3..f889fe0 100644
--- a/lib/hostasyn.c
+++ b/lib/hostasyn.c
@@ -93,6 +93,21 @@ CURLcode Curl_addrinfo_callback(struct connectdata * conn,
 
   if(CURL_ASYNC_SUCCESS == status) {
     if(ai) {
+#if defined(ENABLE_IPV6) && defined(CURLRES_ARES) /* CURLRES_IPV6 */
+      Curl_addrinfo *ai_tail = ai;
+
+      while (ai_tail->ai_next)
+        ai_tail = ai_tail->ai_next;
+
+      /* Add the new results to the list of old results. */
+      ai_tail->ai_next = conn->async.temp_ai;
+      conn->async.temp_ai = ai;
+
+      if(--conn->async.num_pending > 0) {
+        /* We are not done yet. Just return. */
+        return CURLE_OK;
+      }
+#endif
       struct SessionHandle *data = conn->data;
 
       if(data->share)
@@ -111,8 +126,49 @@ CURLcode Curl_addrinfo_callback(struct connectdata * conn,
         Curl_share_unlock(data, CURL_LOCK_DATA_DNS);
     }
     else
+    {
+#if defined(ENABLE_IPV6) && defined(CURLRES_ARES) /* CURLRES_IPV6 */
+      if(--conn->async.num_pending > 0) {
+        /* We are not done yet. Clean up and return.
+	   This function will be called again. */
+        if(conn->async.temp_ai)
+          Curl_freeaddrinfo(conn->async.temp_ai);
+        return CURLE_OUT_OF_MEMORY;
+      }
+#endif
       rc = CURLE_OUT_OF_MEMORY;
+    }
+  }
+#if defined(ENABLE_IPV6) && defined(CURLRES_ARES) /* CURLRES_IPV6 */
+  else
+  {
+      if(--conn->async.num_pending > 0) {
+        /* We are not done yet. Just return. */
+        return CURLE_OK;
+      }
+
+      if(conn->async.temp_ai) {
+        /* We are done, and while this latest request
+           failed, some previous results exist. */
+        struct SessionHandle *data = conn->data;
+
+        if(data->share)
+          Curl_share_lock(data, CURL_LOCK_DATA_DNS, CURL_LOCK_ACCESS_SINGLE);
+
+        dns = Curl_cache_addr(data, conn->async.temp_ai,
+                              conn->async.hostname,
+                              conn->async.port);
+        if(!dns) {
+          /* failed to store, cleanup and return error */
+          Curl_freeaddrinfo(conn->async.temp_ai);
+          rc = CURLE_OUT_OF_MEMORY;
+        }
+
+        if(data->share)
+          Curl_share_unlock(data, CURL_LOCK_DATA_DNS);
+      }
   }
+#endif
 
   conn->async.dns = dns;
 
diff --git a/lib/urldata.h b/lib/urldata.h
index 62dabeb..df34e5b 100644
--- a/lib/urldata.h
+++ b/lib/urldata.h
@@ -468,6 +468,8 @@ struct Curl_async {
   bool done;  /* set TRUE when the lookup is complete */
   int status; /* if done is TRUE, this is the status from the callback */
   void *os_specific;  /* 'struct thread_data' for Windows */
+  int num_pending; /* number of ares_gethostbyname() requests */
+  Curl_addrinfo *temp_ai; /* intermediary result while fetching c-ares parts */
 };
 #endif
 
-- 
1.7.1